I can tell you how this turned out. I bought this concertina from Meg, can't place the date by memory, but essentially shortly after her last post on the topic.
At the time, Meg had a solid offer of $7,000 from Ireland, but she was uncomfortable with the financial and shipping aspects of an international sale. Since I'd tried it before, she reached out to me to ask if I'd make a counter offer. I lived within 40 miles of her, so it was no trouble to visit again. I set $6,500 cash on the table and she accepted it.
I've never regretted the purchase, and in fact, it sold for less than it is currently worth to me. I'd happily pay $7,500 for it now, perhaps even $8,000, knowing it as I do, if it were for sale from another today. It has a distinctive, slightly strident sound that I'm quite fond of. I own other premium instruments but this Dipper is my favorite.
I discussed it with Colin after buying it. Meg had purchased it through Lark in the Morning in Seattle and they listed it as a Professional County Clare, with a price about $1,000 higher than the standard County Clare that they also listed in their catalog. Colin said that he had an agreement with the owner of the business in those days and provided two instruments a year to Lark for them to sell. He said that the Professional model has better reeds than the standard County Clare, in fact his exact words were that he put his very best reed-work in that model. I had owned a standard model County Clare previously and I could clearly hear the difference. I also noted that this Professional model has longer reeds for the lowest notes. I seem to recall that the lowest reeds on my standard Clare were weighted.
I'm very happy with this instrument.