If you ever rolled money over to a 457(b) that did not come from native funds in a 457(b), the 457(b) plan is required to track the rolled over funds separately since distributions of those funds are subject to an early-distribution penalty, reported with code 1 if the distribution occurred before age 59½. The fact that you received two Forms 1099-R from the 457(b) suggests that your distributions came from a combination of native 457(b) funds and rolled over funds.
The separate tracking is an anti-abuse provision to prevent one from rolling in funds from, say, an IRA, and then trying to avoid the early-distribution penalty on those funds by distributing them from the 457(b) instead of directly from the IRA.
