My own take on it is that the numbered set was probably intended for distribution in 1970 and then pulled back for some reason. A possible causative action may have been related to the players and teams depicted on the cards. If we look closely at the four extra panels in the numbered set, we can almost see a pattern develop.
The #1-3 panel with Tim McCarver, Frank Robinson and Bill Mazeroski is up first. McCarver broke a finger in early May of 1970 and was out for a long stretch. Robinson seems like he was reasonably healthy and intact in 1969 and 1970 but Mazeroski was slowing down and only played 67 games in '69 and lost his starting job at second to Dave Cash. Depending upon the timing, the McCarver injury could have caused Topps to yank this panel or combined with Maz's decline it may have been deemed too unappealing to market this trio in 1971. Here is McCarver:
Cards #13-15, depicting Ferguson Jenkins, Al Kaline and Ken Harrelson would seem to be no-brainers to keep in the 1971 set. Jenkins and Kaline had no issues that would preclude their being in a 1970 set but the Hawk broke a leg in spring training that year and missed all but the end of the season. His 1970 season saw him play in only 13 games even though he would play one more year. Solution? Pull the entire panel! Here's what coulda been:
#34-36 displays Maury Wills, Tom Seaver and Tony Oliva. Seaver was the hottest pitcher in the game from 1969-71 and Oliva had solid seasons all three years as well. This leaves Wills as our likely culprit but no, he is properly shown as a Dodger:
and had productive seasons in the 69-71 tranche as well. Why this panel was pulled is a mystery, perhaps Tom Teriffic had another endorsement deal that kept him from being in too many Topps sets but really it's just bizarre this panel was excised.
Finally, we have #43-45 with Jim Wynn, Richie Allen and Tony Conigliaro. Tony C of course was fighting his way back from a horrific beaning but it's Allen that caused the problem here. He is shown as a Cardinal, even though I can't find a scan to show it right now,which was all well and good in 1970 but for 1971 he was a member of the Dodgers. The trade to LA happened in October of 1969 and as we already know, Topps was fond of starting Bazooka production in the year prior to issue, so '69 teams for a 1970 release makes sense.
Other than the Wills/Seaver/Oliva anomaly it all makes sense but since this is Topps, there is always something that skews things! Was the numbered set to be a 1970 issue? Based upon the Rickie Allen Cardinals cards, I would have to say yes. What caused the entire set to be shelved is something I cannot explain. If they are truly proofs in numbered form, then they probably came to market through the Card Collector's Company.
More 1971 Bazooka action next time out kids!