Complex sentence: The same Regiment subsequently provided the Queen's Guard in 1958, during the 1990s the Band of the Honourable Artillery Company provided musical support for the the Queen`s Guard and they continue to do so in the 21st century.
Split into simpler sentences: The same Regiment subsequently provided the Queen's Guard in 1958. During the 1990s the Band of the Honourable Artillery Company provided musical support for the the Queen`s Guard and they continue to do so in the 21st century.