I think you can even put all updates in the 01 folder, and it will work. they either all have to be in there or in separate folders from 01-20 as 20 updates is the max allowed. it's from firmware 3.50 that increased the limit from 10 to 20. update debug is part of qa flagging fyi, so just enable it, put an updater folder on the root of the internal hdd, then have 01 through whatever with your updates. and, as I mentioned, updates can be named anything (don't even need an extension).
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though, if installing the same firmware, it may have to be done through the recovery menu (not entirely sure).
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afaik, what allows installing the same firmware is the image version. rebug uses all 9's. I don't know where all that is, but I know it's in the vsh.self at least, and it's part of the spoofing process, because the firmware is in there as well.