Yes.

1. The worlds of VII and CC/CT do not mix. If Sephiroth existed in this world, then wouldnt we hear at least a little bit about Meteor, Midgard, and all these other goings on?
2. The correct name for CC/CT's Masamune is Grand Lion.
3. Masamune is used in tons of other games, and is never the same sword twice.
4. Grand Lion in CT was a broad sword anyway. I know it can change, as it did when Doreen joined them and it became the Grand Dream Lion (I think that's the right name), but I doubt it would turn into that slim, long katana Sephiroth weilded in VII.