[July 14 - ZIP seems to have fixed these all]
There are some duplications of apparently identical DVDs in the ZIP database, probably due to their getting multiple sets of information from their suppliers. Some really seem to be in stock under both inventory IDs, in other cases one may be a discontinued UPC code, probably showing a perpetual "On Order". Hopefully ZIP will be able to merge duplicates together to avoid confusion and separate waitlists for the same DVD.
There is a 6-disc set of "Dr. Who - The Key to Time", which has the standard 1-page inventory listing. The inventory numbers range from 102970-102975, but as is usual with ZIP sets all but the first one redirect to a common page using the first disc's inventory ID#, in this case 102970. However, there also seems to separate set of inventory listings for the 6 titles. My guess is that they got info for this set from two sources, and in one case created the standard multi-set entry and in the other created 6 separate entries. The problem is that it is likely that people with a disc from the first group in their queue likely won't get the equivalent disc from the second group if it is available. Presumably these should be merged into one set of listings.
The two disc "Once Upon A Time In America" seems to be in inventory twice, as 114653/114654 and 113273/113375
Apocalypse Now (100766 and 113791)
The Kieslowski "Three Colors" set of films (Blue/White/Red") has two separate listings. The first starts at inventory #114927 as is still listed as "On Order", while the second one starts at #114944 and seems to be available. [June 29 - 114927 set deactivated]
Taxi Driver (109583 [available] and 113656 [on order]). Looks like two different sources of info, but I think the same DVD. [June 29 - 113656 deactivated]
"The Crying Game" - #114966 is in stock, #114763 is listed as "On Order". [June 29 - 114763 deactivated]