This should be explained in the notes for the section 'Comparing1' - if you cannot see the following line there, please reply in this discussion, as the notes have been updated over the past few days to include it:
- "(Note - this usage of cyn is completely separate to its meaning of 'before'.)"
cyn in this usage means 'so' or 'as'. In the case of cyn lleied, yes, the two words do remain separate. With cystal, cynddrwg, cymaint the cyn element has become embedded.