The limitation is different in different Contracting States because the claims forming the basis of the limitation procedure were different in different Contracting States. This situation would occur where the patent has different claims for different Contracting States, because of national prior rights or prior art under Art. 54(3) (for patents granted before 13.12.2007 or for patents granted in respect of European patent applications pending at that time), or where under Art. 61 a partial transfer of rights has taken place (Rule 18(2)).
The requester might wish to apply a limitation already introduced for one or more Contracting States to the other Contracting States, or to bring the claims into line with each other for a different reason. If this results in a single set of claims for all Contracting States, and the substantive requirements are met separately for each different set of original claims, then the request would be allowable.
Note that it would also be possible that the circumstances of this paragraph and paragraph D‑X, 10.1 coexist in a single request.