If the former boss is truly a "doulbe ess oh bee" (spelt backswards), then I suggest these alternatives:
First is to have the company personnel office write the letter, attesting to the fact the hours were documented. Lacking such an office, go up the ladder to the boss's boss.
The second is to write the letter yourself, as "training director" (or whatever your title was), attesting to his time and training.
After all, it is common for a man to have many supervisors over four years.
Either letter ought to satisify the board. They are concerned with the man's training and experience, not with who is exactly where in the chain of command.
