The first bird I saw was W:195, the bird I'd seen back in 2015. It was in pretty much the same place as in 2015, namely on top of an ice cream shelter on the harbour front in St Ives. It was originally ringed in St Ives in June 2014, and had been reported from there on several occasions when I reported it then. Hopefully, it'll have been reported a few more times in the last 2 years.
The other bird, a new one for me, was W:186. This bird was also present in and around the harbour in St Ives, heling itself to scraps of food!!
The birds were ringed as a part of a scheme, lead by the West Cornwall Ringing Group (see here). I'll email them my sightings and update the blog when I hear back from them.
UPDATE: I heard back the Ringing Group today (many thanks for the quick reply), and both birds were ringed in St Ives in June 2014. They've both been reported many times since ringing, mainly in and around St Ives, and the Hayle Estuary (4km), but W:195 did also go on a day trip to Mousehole (13km away) in January 2017.