People who manufacture crystals print the cans with the frequecy of the crystal. In the case of the TX, this is the frequency transmitted to air. Because of the way RXs work, the RX crystal is offset by 455KHz, and will be printed as such.
In order to create confusion, the marketers of the crystals (ie set manufacturers) stick little labels to them. Very often, the RX is LABELLED with its matching TX frequency rather than the frequency of the crystal itself. Sadly, the only information I have been able to turn up on the web details the TX frequencies - the manufacturers are very reclusive about giving useful information, probably a facet of their continuing effort to lock you into their particular range.
If the FM sets use the same IF strip as the AM sets, the offset will be the same and same crystal will be correct for both. The difference will come in with dual conversion receivers.
Any pointers to websites with useful frequency listings gratefully received.