Who's bidding?

Have you ever asked yourself: who are the collectors that I am bidding against? A search in ACSearch turned up some interesting provenance for this coin. I purchased it in October of 2021 from Naville. Searching for "Valerian Eirene" in ACSearch I noticed a coin that I thought I recognized...sure enough it was my coin, but not from the auction where I purchased it.

Roman Egypt, Alexandria, Valerian I, AD 253-260, BI Tetradrachm (23.8mm, 10.44g, 12h), dated RY 3 (AD 255/256)

Obv: Laureate and cuirassed bust right

Rev: Eirene standing facing, head left, holding olive branch and scepter; L Γ (date) to left

Ref: Köln 2859; Dattari (Savio) 5150; K&G 88.17; Emmett 3708.3

An image search turned up a few more - none from the auction house that I purchased it from:

The varied scores (all matching the same coin) show how sensitive the algorithm is to different photos. These are all photos of the same coin and even the photo I searched with only shows 9.1 as the similarity score - that seems surprising - why not 100% - perhaps i used a different size image or something was lost or changed as I saved a jpeg?
 

For this coin - here's who was bidding for this coin 5 "collectors" owned my coin in the 30 months before me:
 

- Naville Auction 68, Lot 191 3-OCT-2021 (starting price 30 GPB, sold 95 GBP)

- Naville Auction 56 Lot 257 22-MAR-2020 starting price 25 GBP, this auction lists: Ex CNG E-sale 448, 2019, 339 and seems to ignore the sale or attempted sale at Savoca, no hammer price.

- Savoca Auction 4 Lot 635 12-JAN-2020 starting price 40 GBP no reference to prior owner, no hammer price.

- CNG eAuction 448 Lot 339 17-JUL-2019 starting price 60 USD no reference to Roman owner, no hammer price.

- Roma E-Sale 53 Lot 07-FEB-2019 starting price 48 GBP, no hammer price recorded.

- A private North American collection (not much revealed by this description)
 

In 31 months this coin had 6 owners. Note: I use the term "owner" lightly - it seems to have changed hands mostly between auction houses or perhaps one owner shopping multiple auction houses and failing to sell.

The weight listed fluctuated a bit from auction to auction: 10.47g, 10.44g, 10.50g, 10.92g - clearly someone wasn't measuring too carefully or scales not calibrated well. CNG got it right by my scale; 10.44g is what I weighed today. Diameter fluctuated between 23.5mm and 23mm between auctions - I measure it as 23.8mm.

The reference : Dattari (Savio) 5150 carried across all auction houses. The number of exchanges on this coin seems a little unusual and does suggest to me some pricing support from competitors attending each other's auctions or at least buying each other's unsold inventory.