Hi nxt,
I've been thinking about that.
It is hard to reconcile the fact that they seem to sell apparently functional software to SMBs on a continuous basis with the fact that major contracts require customisation. TCG is meant to be all about interoperability.
My guess is that, yes, there may be residual incompatibilities to iron out; but also, that Wave is probably developing new general capabilities against its more prolonged and particular transactions.
Also bear in mind - it may be the case that someone has to engage with incumbent software providers to harmonise their offerings with TCG prerogatives. My hope is that Wave's work upfront results in a long run benefit, such as the opening of the market or, better yet, a barrier to entry.