Most 135 training/testing says something like this:
§135.343 Crewmember initial and recurrent training requirements. No certificate holder may use a person, nor may any person serve, as a crewmember in operations under this part unless that crewmember has completed the appropriate initial or recurrent training phase of the training program appropriate to the type of operation in which the crewmember is to serve since the beginning of the 12th calendar month before that service. This section does not apply to a certificate holder that uses only one pilot in the certificate holder's operations.
Before that though, 14 CFR 135.323 states:
§135.323 - Training program: General.
(b) Whenever a crewmember who is required to take recurrent training under this subpart completes the training in the calendar month before, or the calendar month after, the month in which that training is required, the crewmember is considered to have completed it in the calendar month in which it was required.
So let's say that I completed initial training in March. This says that if I complete recurrent training in February or April that they consider the training to have been completed in March.
So what happens if a year passes and recurrent training is due. I don't make it in February or March, but the company schedules me for recurrent training towards the end of April. Is it legal for me to fly in April before I go to recurrent training?
At this point, I don't meet 135.343 (because I am no longer within the required 12 calendar months) but I haven't been to training yet, so 135.323 doesn't really apply.
From my interpretation of the regulations I would say no, however every 135 company that I have ever flown for continues using pilots until they go to school, or stop flying at the end of the late grace month if they still haven't gone. The POI's have never complained about it. I feel like I must be missing something.
Is it legal for me to fly 135 trips during the late-grace month?? Note that the same the same scenario applies to 61.58 PIC checks as well, which also have a provision to train during the eligibility period (the month before or the month after it is due).