With regard to missing and appointment and escorting the Soldier I cannot tell you what is appropriate. If you were directed to escort the Soldier and missed the appointment as a result of the direction/order, you most likely have a case against the Article 15. But this will be for a JAG representative to discuss with you.
You are correct they cannot backdate a counseling statement. They can reconstruct a counseling statement and ask that you sign it but you are under no obligation to do so. Please check out the following Q&As that may provide you additional information.
- Can a leader back date a counseling?
- Should I refuse to sign counseling statements I do not agree with?
- When do I fill out the assessment portion of the 4856?
- What do I do when a Soldier refuses to sign?
- Can my squad leader back date a counseling?
- What do I do when a Soldier checks disagree?
With regard to not being counseled monthly or otherwise I am not sure it has any real bearing on the issue. While it is inappropriate that you have not be counseled regularly and it is something you could bring up during an Article 15 proceeding, it has no bearing on missing an appointment.
Leave as a benefit
With regard to leave. To my knowledge a Flag only stops advanced or excess leave. Normal leave is a benefit (meaning it is earned as part of your compensation), not an privilege. Therefore it can only be stopped in rare cases. For example, the command can disapprove leave if they could prove you are a flight risk for AWOL.