True Paul, but in the case of some Boss effects the first buffer is entirely there as part of the FET switching bypass circuit and so in the case of this one for instance, if you leave the first buffer and just remove the FET switching you have two buffers in series before the actual effect which would seem pointless.
Experimenting with the inclusion or exclusion of buffers is one of the things DIY is all about IMO, and judging by the comments for some layouts like the Son of Clay Jones it's worthwhile, even if it means the signal hitting the gain stages isn't as predictable by their exclusion. But in this one, because one buffer remains it should still be pretty close but with a reduced layout size.
And yes this one should be 1590B friendly so I'll add it to the list.