OsmoBTS sends SI1 even if it is not specified/needed
TS 45.002 Chapter 18.104.22.168 clause ii) states
"System Information Type 1 need only be sent if frequency hopping is in use or when the NCH is present in a
cell. If the MS finds another message when TC = 0, it can assume that System Information Type 1 is not in use."
However, OsmoBTS always will transmit the contents of the SI1 buffer. So if a BSC would not send a valid BCCH FILLING for SI1, then we would transmit no system information at all.