AIUI, the bridge firmware divides the drive into several sections.
key sector + "hint" sector
AIUI, the firmware expects to find the key sector at a certain offset from the end of the drive. Let's call this LBA X. Now that the drive has been truncated with a HPA, the firmware is looking for the key at LBA X - (1953525168 - 1953523055), ie X - 2113. That is, you have located the key at LBA 1953517576 whereas the firmware is looking for it at 1953515463. If you are feeling adventurous, you could copy the contents of LBA 1953517576 to LBA 1953515463, but only if the latter sector is empty, and only after cloning the drive. Then use the original bridge to decode the data. Of course you will then have the problem of the truncated file system and corrupt partition table. If the other party has formatted the drive as well as initialising it, then you will also have a corrupt boot sector and MFT.
Normally you would remove the HPA, but I'm not aware of any tool that can do this via USB. After removing the HPA, you could examine the tail end of the drive and search for BIOS related text strings (eg "AMIBIOS" or "AWARD"). This will confirm where the HPA originated.
My next question is, why did the bridge firmware originally identify itself as an Initio device? Was it because it could not find the VCD, and was this because it was looking for it in the wrong place? If the firmware expects to find the VCD at a certain offset (Y) from the end of the drive rather than at an absolute sector address, then perhaps it is now looking for it at Y - 2113. Moreover, since you have updated the firmware, and assuming that the update also writes to the VCD, has the update now been written to sector Y or to sector Y - 2113? If the latter, then this will will have overwritten the tail end of the user area. Worse still, if you now remove the HPA, will the firmware once again be unable to find the VCD, in which case will it again identify itself as an Initio device and require a second update?