If you assume perfect determinism (and having the necessary knowledge to confirm the question at hand), then your claim say is correct. Opinion does not matter.
The simplest example of such a case is mathematics. No matter how many experts agree that 1 + 1 = 3, it doesn't matter until there is irrefutable proof.

However, real life is usually not as cut-and-dry as we would like. Therefore, we have to give way to imperfections. These can take several forms, for different reasons:

• Because we don't know conclusively - In absence of a conclusive answer, a reasonable quorum among leading experts is statistically the most likely answer. If a pro tempore answer is needed before a conclusive answer has been found, the quorum tends to yield the best available answer.
• Because of local context - The given answer might not be universally correct, but for the given question in its given context, it suffices. For example, we calculate the circumference of a circle using pi, even though we don't yet know it's exact value. We use an approximation, one that is proportionately accurate based on what we need right now (= the context).

I don't agree that these cases should be considered fallacious, as long as they don't outright and explicitly claim to provide the final and complete, yet unproven or incorrect answer.

For example, if a teacher were to state:

"Pi is equal to 3.14"

If this is said during a beginner's class on geometry, I wouldn't call that a fallacious statement.This falls under the second bullet point: it suffices for the current context.

If that teacher were to state:

"Pi is [all currently known digits of pi]"

That wouldn't be fallacious either, as the teacher would adhere to the first bullet point: giving the best available information.

However, were that teacher to say:

"Pi is exactly equal to 3.14"

I would call that fallacious, as it makes an outright and explicit claim that is unfounded (at best) or a conscious lie (at worst).

To summarize
Your claim holds true in a setting of formal determinism, but casual human speech does not meet such a standard of formality. People omit quantifiers when they are contextually unnecessary, leading to formal imprecisions but as formality is not the topic at hand, none of the conversation's participants suffer from the imprecision.

If you assume perfect determinism (and having the necessary knowledge to confirm the question at hand), then your claim say is correct. Opinion does not matter.
The simplest example of such a case is mathematics. No matter how many experts agree that 1 + 1 = 3, it doesn't matter until there is irrefutable proof.

However, real life is usually not as cut-and-dry as we would like. Therefore, we have to give way to imperfections. These can take several forms, for different reasons:

• Because we don't know conclusively - In absence of a conclusive answer, a reasonable quorum among leading experts is statistically the most likely answer. If a pro tempore answer is needed before a conclusive answer has been found, the quorum tends to yield the best available answer.
• Because of local context - The given answer might not be universally correct, but for the given question in its given context, it suffices. For example, we calculate the circumference of a circle using pi, even though we don't yet know it's exact value. We use an approximation, one that is proportionately accurate based on what we need right now (= the context).
• Because it is not universally deterministic - Your software engineering example applies here. "Best" is subject to implicit considerations such as time, effort, complexity, maintainability, volatility, personal experience of the speaker, ... but these quantifiers are omitted in favor of giving what is genuinely assumed to be a commonly agreed upon balance of the omitted considerations. The true "crime" here is doing away with these pedantic quantifiers in favor of keeping the conversation lighter and easier to grasp. Could these considerations have been expressed? Sure. Would the conversation's participants appreciate it, or have need of it? No. This is a variation on the second bullet point, where the conversation's participants mutually agree on a local context which precludes the need for explicitly mentioning strict modifiers.

I don't agree that these cases should be considered fallacious, as long as they don't outright and explicitly claim to provide the final and complete, yet unproven or incorrect answer.

For example, if a teacher were to state:

"Pi is equal to 3.14"

If this is said during a beginner's class on geometry, I wouldn't call that a fallacious statement.This falls under the second bullet point: it suffices for the current context.

If that teacher were to state:

"Pi is [all currently known digits of pi]"

That wouldn't be fallacious either, as the teacher would adhere to the first bullet point: giving the best available information.

However, were that teacher to say:

"Pi is exactly equal to 3.14"

I would call that fallacious, as it makes an outright and explicit claim that is unfounded (at best) or a conscious lie (at worst).

To summarize
Your claim holds true in a setting of formal determinism, but casual human speech does not meet such a standard of formality. People omit quantifiers when they are contextually unnecessary, leading to formal imprecisions but as formality is not the topic at hand, none of the conversation's participants suffer from the imprecision.

I could (tongue in cheek) turn this on you and claim that the true fallacy here is your expectation of a casual conversation conforming to a formal standard of universal determinism, which is hardly if ever the case.