How did Birds 2 Faststamps get to Yeovil Post Office ?

As reported here, the upgrade to version 2 of the Post and Go machines has produced 40g versions of the Birds 4, Birds 3 and even Birds 2 Faststamps.

Now we've evidence that Birds 2 was being sold at Yeovil just after before* and after Christmas - and that office wasn't even on the Birds 2 original list.  So how did this arise?  Are there still stocks at Swindon awaiting distribution?
* We've been told of Yeovil sales on 23 December.

 Thanks to Roy for this report!