For training with a grace month, is it legal to fly in the month after training expires before going to school? 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).
Yes, the FAA issued a Letter of Interpretation from their Chief Counsel in May 2015 which covers Section 61.58 proficiency checks and specifically addresses this issue. 

It says that a pilot may continue to act as PIC during the grace month under Parts 91, 121, and 135.  It says (in part, and emphasis added by me):




  Section 61.58(i) states that, if a pilot completes the proficiency
  check in the calendar month before or the calendar month after the
  month it is due, "the pilot is considered to have taken it in the
  month in which it was due for the purpose of computing when the next
  pilot-incommand proficiency check is due." 
  
  You have asked whether the language in paragraph (i) creates a "grace
  month" during which a pilot whose currency has lapsed under paragraph
  (a) may continue to act as pilot in command. The FAA has previously
  stated in a legal interpretation that § 61.58 includes a "grace month"
  for purposes of complying with the 12- and 24-month proficiency check
  requirements. We did not explicitly state, however, that a pilot may
  continue to act as PIC during this grace month. Legal Interpretation
  to Sean Conlin (Feb. 24, 2000). We have indicated, however, that
  similar provisions in parts 121 and 135 create a "grace month" during
  which a pilot may to continue to act as PIC during the month after the
  pilot's currency has lapsed? Legal Interpretation to Gregory S. Winton
  (2006), Legal Interpretation to J. Dennis Vanatta (June 25, 1996). 
  
  The FAA intended the grace month to limit disruptions in operations
  conducted under parts 121 and 135 by accommodating pilots who are
  unable to complete recurrent training requirements in the month they
  are due. At the same time, the FAA did not want operators to use the
  grace month as a means of regularly extending a 12-month proficiency
  check to a 13-month proficiency check. For that reason, a proficiency
  check under part 121 or part 135 that is completed in the grace month
  is considered to be completed in the month it is due. The FAA believes
  that the same approach is appropriate for§ 61.58 proficiency checks.
  As such, a pilot may continue to act as pilot in command during the
  month after a§ 61.58 proficiency check is due. However, when a pilot
  completes a §61.58 proficiency check during this grace month, it is
  considered to have been completed during the month it was due for the
  purpose of calculating the next proficiency check.