It is a very considerable factor and they are most certainly going to consider the Interational factor as well, but considering the GBA entries are considered minor entries in the series (Roy was a last minute addition for advertising purposes), especially next to FE3 and FE4, and seeing how Marth and Roy were VERY well received REGARDLESS of the fact that they were from a series alien to us at the time, so to them it may not matter all too much. Again, this does NOT rule out Lyn, but she's not a shoe-in like everyone seems to be convinced either... Also Sakurai's catering toward the West is most likey to consist of franchises that have a significant presence in the West, i.e. Metroid, Kid Icarus (all-time cult classic over here), Punch-Out!!, and hopefully Star Tropics (Western exclusive cult classic).
However, to be fair I might as well also provide some factors in Lyn's FAVOR (and what's wrong with playing devil's advocate every once in a while?). Upon my own research, I found that the GBA titles DID in fact do well in the domestic Japanese market, contrary to the hearsay that's been floating around that they didn't do so well back in the home market. The sales firgures are as follows (Note these are the sales figures for JAPAN):
Fire Emblem VI: Sealed Sword -- 393,000
Fire Emblem VIII: The Sacred Stones -- 298,000
Fire Emblem VII: Sword of Raging Fire -- 293,500
Compared to:
Fire Emblem III: Mystery of the Emblem -- 697,750
Fire Emblem IV: The Ancestral Crusade -- 578,000
Fire Emblem V: Thracia 776 -- 257,500
Fire Emblem IX: Path of Radiance -- 155,750 (Ouch... not as well as we assumed...)
Source:
http://www.vgcharts.org/welcome.php
Unfortunately, the data's not as reliable as far as NA data for Fire Emblem sales is concerned, though FEVIII:TSS sold just under 400,000 and FEIX
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oR sold over 200,000 -- FEVII didn't even show up for some reason, put I'd put it somewhere in between TSS and PoR. Didn't have the data for the PAL regions. At any rate, there's the data - I report, you decide!
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(Sorry, couldn't help but to poke some fun at FOX News...)