The real route length of the NYC subway. Over 400 km?

[I love NY]

On page 155 of (http://web.mta.info/mta/investor/pdf/2020/2019_CAFR_Final.pdf) there is an interesting table of the MTA and there is written that the route length of the NYC subway is 248 miles.

1) But why until 2014 there were 246 subway route miles (NYC subway+Staten Island Railroad) and since 2015 (before 2017 expansions of the 7 and Q lines) they are 259?

2) Is it possible to know how many exact rail route mails has the NY subway? I know that they were 245 miles before expansions of the 7 line (1,5 miles) and the Q line (1,8 miles), therefore the total should be 248,3 miles (399,600  km). We know that the new 1,8 mile tunnel extends under Second Avenue from 63rd Street to 96th Street (https://www.wsp.com/en-SE/insights/new-york-opens-its-second-avenue-subway). But since 2017 it is in operation also a new small segment under the Central Park from 57St -7Th Av station to Lexington Av-63St station. What is the lenght of this tract without calculation the very small part that overlaps with the F line? If it is at least 0,3 miles, the new total should be 248,6 miles and therefore OVER 400 km.

Thank you for the possible reply and excuse me for my incorrect English.