I guess this has been discussed before, but I could not find through SERACH.

I plan to purchase AONE5, however, there are no A or even D available on some sectors(regular F or C is available). In that case, I have to sit on Y if only L is available?

Also, if we book L, and then later D or A become available, can we change them without penalty?

Also, since my total sectors become 18, we want to take 2 sectors out from RTW, and purchase roundtrip separately.
For example, NRT - LHR - LIS - LHR - NBO, and we remove LHR-LIS-LHR and purchase this LHR-LIS round trip separately.
At NRT, we have to show two tickets, one for AONE5 and another for LHR-LIS since we want to go LIS through LHR without stopover.
If we use two tickets, and if NRT-LHR delays, there is no guarantee on second ticket LHR-LIS sector?

Thanks in advance.