This may be the case for zero fare excess, however I cannot see a TOC having a form to fill in for a standard excess.Some staff really don't like issuing excess fares (they may see it as difficult) and some don't mind if there is a value to them, but won't issue them if the value is zero.
I believe some TOCs require a form to be completed and some staff either don't want to bother filling it in or maybe don't know where the forms are kept or some other reason that doesn't really make any logical sense.
Some Mobile TIS require an explanation on your shift sheet for any ZF that you have done but that is it.