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This would be a really good time to buy your SoM expansion, MoM is still better bought at retail but you may not have a chance for that if you want to take advantage of the sale. Why it is a good time? Because in the november update Lothlorien will be decoupled from the moria expansion, we do not know yet wether or not this will affect boxed versions or not.
Keep in mind that SoM requires MoM to be bought. Also this is US only, but it stands to reason EU will get a similar sale in the furture(which might or might not contain Lothlorien depending on wether it happens after or before the november upgrade).
P.S.: If you do not see the sale, it was 11/11(Veterans Day) only. Its a good idea to check the LotRO store around any holidays.