Dear Jasper B.,
That less-than symbol refers to this sentence in
the Type 1 description just above it:
"The overall length is almost always under 31.5", and in some cases it may be even less than 27.5"."
The phrasing suggests that the original overall length of some of the blades that may have been at the short end of the range is now unrecoverable. Because the length is uncertain, it makes sense to indicate this end of the range using the less-than symbol.
I hope this proves helpful.
Best,
Mark Millman