Its interesting that 26% havent upgraded from 1432 yet.
In pool.biblepay.org, we enforce the version must be > 1.4.4.4 btw, so the 26% who did not upgrade are definitely solo mining.

As far as how they are doing it, the mandatory upgrade with 1445 actually was mostly related to govobj propagation + cameroon 1 bus logic.  So, we did make it mandatory so that the sancs upgraded (and we know they did because the sanc protocol version is enforced).  

But getting very specific, 1.4.3.2 will actually still stay in sync and mine technically (because it wasnt a hardfork consensus breaker).  The main reason it was a mandatory was the older versions had a problem with gobject propagation - this basically means those 1432 nodes do not have a complete picture of the daily GSC contract; they are more apt to go out of sync if they miss a gobject; and worse they might not forward a gobject over to a friend node.  We probably should enforce it in the next leisure (by ddossing or banning versions earlier than 1440).  Most likely these miners are not full nodes anyway (meaning they arent sharing the data much) as miners are usually behind their own firewalls (they arent sancs), so the problem is relatively low risk.

But yes we could consider banning them in our next release so they upgrade.

Thanks for pointing this out.

From a mining perspective this should not be causing a problem though since they can't pool mine, they must be self funded abns.

But as far as hitting blocks, the pool is still hitting 33%.  I havent seen a big change recently. 
(So these 3 CPKs are solo mining 25% of the blocks I see.  I wonder how many machines are being used; I don't think we can tell.)