This integer, ranging 0 to 96, reports how many of the previous 15-minute intervals actually have valid stored performance data, defaulting to 32 and capped by device support at up to 96 (24 hours' worth); a device brought online recently will report fewer valid intervals than the full 32 until enough history accumulates. An admin cares because pulling historical error statistics for intervals beyond this valid count will return meaningless or empty data, so this tells them how far back they can actually trust the interval history. For example, a SONET line that came online 90 minutes ago would report roughly 6 valid intervals rather than the full 32, since only 6 complete 15-minute windows have passed.