.
An off-hand reference, like lets say they visit a system seen/mentioned in ENT would be fine something like 'The last ship to survery this system was the NX-01'. Though that would seem weird considering it would have been 100 years ago.
That would actually fit with TOS era, though.
A Taste of Armageddon had a 50 year gap between Valiant and Enterprise visiting Eminiar
A Piece of the Action had 100 years between Horizon and Enterprise visiting Sigma Iotia
Return of the Archons had 100 years between Archon and Enterprise visiting Beta III