I may be a bit slow, I'm not the smartest financial advisor in the shed, but I know there are others out there like me because I've seen many posts on this topic. I think I have figured out the Re-booking "Credit." (you'll notice I used quotations marks around credit.
Many folks, like me couldn't understand why they were seeing less than the expected amount being brought forward from previously Tauck-cancelled tours and applied to an immediate re-booking (a third attempt) and why Tauck Reservation Sales Agents were saying you only get the re-booking credit once. It appeared as though Tauck was clawing back previous credits before applying funds from a cancelled tour to a re-booking.
Well, silly me, I thought the "credit" was like the credit I'm familiar with- one that is deposited to a bank account, credit account, etc.- once it is in your account it is yours. Not so in this case, because it isn't that type of credit. Tauck is applying the term "credit" to what is actually a discount on the cost of the tour, to encourage you to re-book immediately and leave your original payments (deposit and any subsequent payments) on account with them. As everyone knows the "credit" amount depends on whether you have made partial payments ($250 ea.) or are paid in full ($500). The only money carried forward and applied to your new booking, is what you actually paid for the previously cancelled tour. When you re-book the third try of the same tour, any previous "re-booking credit" no longer applies and is not cumulative from tour to tour. I'm not sure I agree with this policy, but at least now I understand it.
Someone please correct me if I am wrong.