If Alvas Marlay is installed as a dance floor with tape (tape down), the Marlay may not be able to be welded later unless the taped parts are cleaned or cut and removed.
Welding of pvc vinyl can get particular. Welded edges must be clean and free of contamination (example: tape residue, etc). The seams must also be cut perfectly with no gaps. Therefore welding fresh, new material on a clean floor is always advised. Welding used material can propose negative outcomes.
A professional pvc-vinyl welder can advise.