Just to be sure, does IRCC absolutely require certified copies of documents for a citizenship by descent chain?

I’m collecting documents for a gen 4 case for my grandmother. Her gen 0 was born in 1949.

I have a clear scan of original gen 0’s 1908 Washington state death cert, clear scan of gen 1’s marriage cert, photo of gen 1’s death cert, scan of gen 2’s 1900 birth registrar and 1991 death cert, gen 3’s marriage cert scan and death cert, and grandmother’s birth cert.

I read somewhere that IRCC requires certified copies, but I just read somewhere else that they only require clear photocopies.

Gen 2’s name on 1900 birth register isn’t very clear anyway, so I’ll be requesting a certified copy of that one just for clarity