Note that "same species as" isn't a transitive relationship. I'l use the (middle) character (of) "=" as "can interbreed with" just to shorten thing; also elipses "...". There may be a chain (geographical one have been observed) of individuals such that along the chain, neighbors can interbreed:
A = B = C = D = E
However, it does not follow that A = E. Were C to be cut out, then there would be two differing "species."
This can happen over time, A1 = A2,....A10000000=A10000001 but A1 cannot interbreed with A10000000. So even though each parent-offspring population is "of the same species," it may happen that the billionth generation would be "a different species" from the first.
"However, it does not follow that A = E. Were C to be cut out, then there would be two differing "species."
Cut out as in removed from the chain? Or nonexistant?
If it's nonexistant that how would you get from A to E?
If A=B=C=D=E and D were cut out, would that also lead to differing species? Or would the final step not occur?