Not true, there are seeded blind lines but there are also a fair number of genuine blind lines. the seeds tend to go, not to the bottom, but to the middle level of seniority as they are too good a clashing tool to ignore. that said the destruction of BLRs being carried out under the auspices of the current BACC chairman has nullified that to some extent.
binsleepen is right. All stage 1 blind lines on the 747 are seeded. Trip lines can also go all the way to the bottom on the 747 which is another good thing for the junior. The bottom of the list is at least getting LAS/PHX/SFO blind lines if they bid for them.
If somebody gets a blank blind line on the 747 after stage 1 it's because they forgot to bid/didn't get awarded any line they bid for.