There has been some recent confusion concerning 'legal' bats. NVSS rules provide that 'Only ASA approved bats may be used in NVSS'. The confusion has arisen because some bats previously approved by ASA are now 'unapproved' ...see unapproved bats
Beyond that issue, some players are using bats 'so old' that the ASA certification has worn off, or perhaps was never there in the first place. George Hersey and several FAS-qualified umpires will decide how these bats may or may not be used, with details to follow shortly.
So, the rule is your bat must have the ASA certification AND not be on the 'unapproved' list. If in doubt, don't use it; AND, you may wish to use a teammate's bat, with their permission.