If Jossverse was built on strict logic, the information introduced in the preview of #6 (vampires can smell pregnancy) would've been enough to exclude Angel from the list of possible fathers. Because no way Spike would've keep his big mouth shut when Buffy was patrolling, or drinking excessively, or carrying Andrew on her shoulders.
But Jossverse isn't logical: writers constantly rewrite their rules. Angel couldn't smell Cordelia's pregnancy in season 4. One can argue it was because Jasmine took measures to hide it. But it means that Joss and Co could go in the same direction about the hypothetical Bangel baby - mystical child, special circumstances, etc.
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About "transcends everything": it was said in spring 2003 when TheWB was agressively hyping BtVS finale as Buffy/Angel reunion. The PR department on TheWB was working hard to create the impression that the final episode was all.about.Bangel. Every article, every interview was focussed on David crossing over to BtVS. Everybody who was interviewed, was supposed to talk about Bangel.
TheWB expected the rating to go up. Instead, they went down for the episode in which Angel appears - End of Days.
http://buffy.tktv.net/Anno7/22.html
Touched - 2.6/4
End of Days - 2.4/4
Chosen - 2.9/5
There was an improvement for the final episode (22% increase) -- but finales of the shows usually get *much* bigger increase in viewership. For example, Dawson Creek that aired the same May 2003 on the same TheWB, got 3.3/5 for the penultimate episode, and 4.8/7 for the finale (45% increase).
http://dawsonscreek.tktv.net/Season6/23.html
I think it was quite a surprise for TheWB that their Bangel hype killed their ratings.
Funnily, the situation got repeated in 2010. DH was agressively hyping Bangel, providing shippers with many quotes to collect - yet didn't manage to increase sales that dropped from 47,013 for #31 to 45,446 for #35.