Altars don’t
have to use relics of the parish’s namesake in the altar, so any relics could have been used.
Another difficulty related to this is that the requirement for relics to be placed in the altar has been removed since the promulgation of the NO. This wasn’t called for by the Council, but you know how these things go.

So some altars, especially the non-fixed type, have been constructed without relics since that time. This causes some difficulty with the free celebration of the TLM since the priest is supposed to kiss the altar at a certain point while saying this prayer:
“We beseech Thee, O Lord, by the merits of Thy Saints, whose relics are here… (Here, he bows and kisses the Altar where a Saint’s relics are enclosed)…and of all the Saints, that Thou wilt deign to pardon me all my sins. Amen.”
“Orámus te, Dómine, per mérita Sanctórum tuórum…quorum relíquiæ hic sunt, et ómnium Sanctórum: ut indulgére dignéris ómnia peccáta mea. Amen.”
Just an interesting side note.