From the great Michael Pettersen at Shure we get this info on Shure's BLX wireless compatibility:
The BLX Wireless Series H8 band (518-542 MHz) was discontinued in October 2015. It was replaced by the H9 band (512-542 MHz) and the H10 band (542-572 MHz). Note the H8 band and the H9 band cover 30 MHz (five U.S. TV channels) whereas the discontinued H8 band covered only 24 MHz (four U.S. TV channels.)
But can a BLX H9 device (transmitter or receiver) be used as a substitute for a discontinued BLX H8 device (transmitter or receiver)? Yes.
The first five frequency groups of BLX H9 and BLX H8 are identical. An H8 device and an H9 device are compatible if they are tuned to a frequency within these five frequency groups.
Arcana - mysterious or specialized knowledge
The Shure Vagabond wireless microphone system was introduced in 1953. The very first Vagabond system sold was purchased by the Archdiocese of Chicago, specifically for use
by His Holiness Samuel Cardinal Stritch during services at Holy Name Cathedral. The installer of the Vagabond was Electronic Systems Company, 1045 South Wesley Avenue, Chicago, Illinois.