Hmm... after rereading volumes 26-28, the daizenshuu seems to make sense based off Toriyama's work. Note that once Freeza reaches his third form, DB reverts to its classic "he's stronger than he is" mode of story-telling, so Toriyama didn't have to worry about PLs. However, what I'm 99% sure the daizenshuu did was notice the following:Xyex wrote: It's still listed as 300k/15million and 6million/12million because that's reasonable.
-Completely ignoring the daizenshuu, we know Piccolo to be exceptionally close to, if not stronger than, Freeza's strength of "over 1 million."
-We also know that Vegeta, after being healed by Dende, is so much greater than Piccolo that he can not only see Freeza's finger beams, but dodge them as well. Goku, unlike Vegeta, is even capable of blocking Freeza's finger beams. With this we know that Goku has completely surpassed the 1 million PL mark, and it is here that the daizenshuu clocks him at 3 million.
-We know that kaioken multiplies the user by the number of times it is used. Ergo, kaioken x20 got Goku a PL WELL OVER 20 million. Since it's obvious that Freeza at 50% was equal to Goku at Kaioken x20, we can also assume that Freeza at 50% also had a PL WELL OVER 20 million.
-Since we know that Freeza was only at half strength, simple multiplication will tell us that Freeza at 100% has a PL WELL OVER 40 million.
-Since SSJ Goku is obviously stronger than Freeza at 100%, we can also conclude that SSJ Goku has a PL WELL OVER 40 million, which would indicate that SSJ is much stronger than kaioken x40, the daizenshuu listing it as being equal to kaioken x50 (or Oozaru x5, if you prefer

Here's where the daizenshuu's PLs come in: Goku at "much stronger than a PL that was waaaaay over 1 million" was estimated at 3 million. The rest was simple math. 3 million x 20 (kaiokens) gets Freeza's halfway mark of 60 million. Twice that is his top at 120 million. Since SSJ Goku is obviously greater than 120 million, which is 40 times greater than his 3 million base, the daizenshuu lists SSJ as multiplying the user's strength by 50, which gets Goku's PL of 150 million.