I suspect this is a carry over from the old UK CAA Performance A exam which used the L1011 as a specimen aircraft. There is a facility there that calculates a max abandon speed on a very slippery or icy runway using a heavily factored ASDR and a V1wet input from another graph. This caveat appears nearly verbatim in the specimen data, CAP 385, and is making the point that, although the data is derived from a V1 wet input the resulting speed is not a V1, but a Vstop. The quote from the CAP is:
'The resulting speed is not a V1 speed for it does not imply any ability to continue the take-off following engine failure and, unlike V1, this speed may be less than Vmcg. Thus take-off on a very slippery runway may result in a 'risk period' between the maximum speed for abandoning the take-off and the normal wet V1 during which, in the event of an engine failure, the speed is too high for a successful stop, and too low for a successful continued take-off'
Is it possible that the authors have mistakenly applied this very specific caveat to all values of wet V1?