NUC – not upwardly compatible – means you’ll have problems using older code and data on a newer version of the code. Most software developers take great pains to avoid NUC changes, or at least document them carefully so that upgraders won’t be stung by them.
But not OpenCart, sadly. This post from long time Zen Cart developer RodG sums it up:
I initially created Better Together for OpenCart to work with OpenCart 1.5. I came back several years later, and found that it needed significant changes for OpenCart 2.0. OK – then came OpenCart 2.3, and again, significant changes were required, and the old code was not upwardly compatible. OpenCart 2.0 to 2.3 is a minor version number update, and there should never be a NUC change in a minor version update (per semantic versioning). Is the expectation really that I should maintain multiple copies of the source for each minor version change? As Rod points out, this would be unique among the open source carts I have worked with.
So a few years pass, and along comes OpenCart 3, which contains – you guessed it – yet more NUC changes. Guys, you’re killing me. But at least there will be compelling business drivers to encourage people to do this upgrade, right?
Well, no, not really, according to Martin Boss of MultiMerch. He says vendors considering upgrading from OpenCart 2.3 to 3.0 face significant drawbacks and limited advantages.
So where does this leave independent software vendors like That Software Guy? In a pretty bad spot – I am actually getting requests to support Better Together on OpenCart 1.x, because people don’t want to upgrade to 2.3, never mind 3.0.