It has often been discussed that Schulz was reluctant to start licensing Peanuts characters out (in rather stark contrast to what ended up happening.) However, it should be noted that once the licensing had started, there was some coordinated effort.
For a blatant example: while Sally had been mentioned in the strip in the spring of 1959, with the announcement of her birth, she was not actually seen until the Sunday, August 23rd, 1959 strip.
The first Sally doll was announced as available in the Tampa Bay Times the following Thursday.
(In pulling up that strip, I noticed the following ad in the ad space bellow it:
That ad musta been there awhile, as the 65th anniversary passed six years ago.)