USCIS released a policy memo that clarifies the requirement that the qualifying organization employ the principal L-1 beneficiary abroad for one continuous year out of the three years before the time of petition filing.
Specifically, this Policy Memo explains that:
1) the L-1 beneficiary must be physically outside the United States during the required one continuous year of employment (although in certain cases brief trips to the United States do not interrupt, or break, the one continuous year); and
2) the petitioner and the beneficiary must meet all requirements, including the one year of foreign employment, at the time the petitioner files the initial L-1 petition.
Source: AILA Doc. No. 18112933.