The 2000 2 pack and 2100 4 pack seem to be the same thing except 2 and 4 pack (both packs say 2100).
An interesting point, it's commonly claimed on the other placethere are only 4 makers of LSD batteries although I haven't ever seen great evidence for this. The Sanyo Eneloops (now comes in multiple flavours) which are made in Japan, the Maha/PowerEx Imedion which come in 2100 (rated min 2000) and 2400mAh (rated min 2250) capacities and are made in Taiwan, the GP ReCycko (Turnigy and Kodak Precharged are believed to be this) which only come in 2100 mAh which are made in China and tend to be a little fat, and the Yuasa-Delta (Panasonic, GS Yuasa, Rayovac Hybrids and blacktop Duracell) which come in 2100 and 2500 capacities and are also made in China.
Both the Eneloops and Imedions have white tops whereas the other two have black tops. (Well not sure about the newer higher capacity etc variants.) http://www.candlepowerforums.com/vb/showthread.php?218956-The-different-varieties-of-LSD-cell
The interesting thing is these are white tops, but labelled as made in China. There are a few others I've seen like this e.g. Camelion https://budgetlightforum.com/t/-/380
and some Ultralast Hybrio
When is a Hybrio not a Hybrio? | Candle Power Flashlight Forum
Uniross Hybrios are Eneloops...? | Candle Power Flashlight Forum…
(Some UNiROSS Hybrio look and perform like Eneloops despite being labelled as made in China)
They look somewhat similar to Imedion (small button top with no vent, ridge near top) but Imedion are always marked as made in Taiwan. No one really seems to know much about these variants. I note from eneloop vs. Kodak Pre-Charged Voltage Maintenance | Candle Power Flashlight Forum it seems there are other Unilast/Uniross Hybrios which are different again and from the description seem to be different from any of the other so it’s rather confusing.
The 2500mAh and 2100mAh rated capacities seem to be similar to the Yuasa LSD variants despite being white top (from what I can tell the 2500mAh Yuasa branded ones are black tops too). Perhaps they’re from Yuasa but a different factory? (There was some suggestion the Hybrios were Yuasa.) Or perhaps there’s more LSD manufacturers by now.
P.S. I came across http://www.candlepowerforums.com/vb/showthread.php?312022-Fake-Eneloops while researching. I have to admit to laughing when it was suggested the (minute number of) people who can actually recognise the old Eneloop design would matter to Sanyo.