Both Collector Levels are guaranteed numbers 2 - 51, but only if all 50 rewards are claimed. For example, if only 30 Collector Levels are claimed, those backers will have copies #2 - #31, and individual backers at the Print Supporter levels will start at #32. Retail store levels pick up the numbering after individual backers.
Note that the US and International Collector Levels are combined. Backers from both rewards work from the same 50 copy pool of numbers.