You need to remember how cards were produced by the Carta Mundi / WOTC alliance. Carta Mundi utilized sheets that contained 121 cards (11 x 11). I seem to remember that the cards in the starter decks were random except the Machamp.
If starter decks were like theme decks, which were usually 60 card decks, they would print all the cards (rares, uncommon, common and energy) for 2 complete decks on the same single print sheet. That sheet would also contain some sort of filler card on it. It would look just like the pokemon sheet I recently described here: www.elitefourum.com/t/a-pokemon-collectible-you-may-have-never-seen/19096/1 The only modification would involve holo rares, which would be printed separately on a large holo rare sheet and would need to be added later.
But if starter decks had random cards pulled from regular production, then it meant pulling cards from the holo rare sheets, the regular rare sheets, the uncommon sheets, the common sheets and the energy sheets. Since base set didn’t have 121 different cards of any rarity, this means that there were multiple copies of each card on a sheet (think back to the Fossil holo rare sheets given away in the Kay-B-toy promotion). What happened was that one or more copies of the original red-cheek artwork were not replaced by the yellow-cheek artwork when the base set common sheets were initially printed. At some subsequent point the artwork was changed so that in later printings only the yellow-cheek variation was printed. If the first printing had equal red cheek and yellow cheek counts, then there were probably 2 copies of each (4 pikachus total) on the common sheet. You would expect either 3 or 4 copies of every common to get 32 different common cards onto a 121 card sheet.