Didn't have enough fasters at the beginning of the service, now do (or might): do you change over to the fast-day liturgy?

Question

On a public fast you only do the liturgical changes (like Avinu Malkeinu) if you have at least six actual fasters present. If you don't have that quorum at the beginning and therefore start doing a regular weekday service, and then more people come in, do you change over? What about if you had already begun the torah service with the regular daily reading (assuming the fast day was also a torah-reading day in its own right, like today was)?

Does it matter if there is uncertainty about the new arrivals, so you don't know if you definitely have quorum now?

(This happened at the shacharit I attended today, though not during the torah service.)

Answer 1

In terms of the Chazzan's reciting Aneinu during his repetition, the Mishna Berura (119 sk 18) discusses the case where the requisite quorum of individuals fasting is either established or lost between the start of the repetition and the recitation of Aneinu (as blessing 8 of 20). He rules that if the quorum was established during that time, the Chazzan may recite Aneinu in its proper place. If the quorum was lost during that time, he may no longer recite Aneinu in its proper place, but he may still recite it during Shema Koleinu (blessing 16 of 19) similar to the way individuals do at Mincha. He makes no mention here of the issues surrounding the Torah reading.

Answer 2

Nit'ei Gavriel (Bein Hametzarim 11:5) discusses a similar case (in connection with Minchah, but I'd assume the same applies to Shacharis). In short, he says that each of these things should be made up where possible: the chazzan can say Aneinu in his repetition of Shemoneh Esrei (even if there weren't the proper number of people fasting when they had said the silent one), and they should read Vayechal after Tachanun.

I'm not sure, though, about the case in the second part of your question, where they had already read the weekly Torah portion at Shacharis. Conceivably in that case indeed they wouldn't read Vayechal too, because there are supposed to be only three olim. One possibility might be to read Vayechal without any blessings, although I don't know a source that says so. (If they had only started reading the regular portion - say for example they only read the kohen's aliyah - then conceivably they could then take out a second sefer Torah and divide Vayechal into only the two remaining aliyos, although again I don't have a source for that.)

Answer 3

I can not imagine that you would do a fast day service if the community is not fasting, and I can not imagine that you would do a normal week day service if the community is fasting, even though the rest of the nation is not.

Doing otherwise, to me, just shows a complete non-belief in what you are actually doing.