Experience from a recent LLONE4 with paper tickets is that all the airlines
we used did not require a ticket to be reissued after a date change. None
of our segments were open dated.

We changed dates by phone, without reissue for IB, LA, QF, CX,
BA, BA/BMed, and BA/EI.

When changing a couple of segments with a Qantas agent they indicated
that BA may charge us for a reissue at checkin (for the BA segments), but
this didn't happen.

As stated here on FT, it may be best to confirm dates for
segments instead of leaving them open, this seems to offer more protection
in the even that a route is canceled or changed.