Thanks for your reply. I have been trying many different ways, but that does not seem to be what is used in practice. For example, assume the curve date is 4/15/2019, the last publication date is 3/11/2019, the last fixing date is 2/1/2019, the option payment date is 4/17/2020 with corresponding fixing date 1/17/2020 and publication date 3/10/2020. The time to expiry for this 1Y Cap in BBG is 9.5 month. I cannot figure out a reasonable way to explain that.