It get pretty weird when you start to log on and write about mixes of particular song. I suppose this is Beatles information that some of us enjoy since a lot of us want to have as many variations in our collection as possible. Let me try to sort this out a bit:
First off, it was decided by the Beatles (mainly Paul) that the solo in the song would be played through a piccolo trumpet similar to one that Paul - the composer of the song - had heard on the BBC 2's "Masterworks" series. The solo and a coda was played by David Mason and added to the the third track of the four track tape. The woodwind instruments were taken out but the previous brass was left in the choruses. Mixing of the song was attempted once the overdubs were completed.
On January 17 1967 in Studio 2 at EMI, George Martin and company mixed the song in three attempts with the last attempt being sent to North America and Capitol Records used this mix on their promotional singles. This mix uses the trumpet coda at the end of the song. (RM11).
One week and a day later on January 25, further mono mixes were attempted and this time the trumpet coda was removed from the song and copies of this mix (RM14) were sent to North America and Capitol Records with the instructions to use this mix for the commercial single.
"Penny Lane" was not mixed nor stereo until after the break up of the group. The commercial version on North America's Capitol LP "Magical Mystery Tour" originally had the song in duophonic or in fake stereo with the highs in one speaker and the lows in the other speaker. The true stereo mix was completed in 1971 and first used on the West Germany Apple LP "Magical Mystery Tour". The current commercial CD also uses this stereo mix.
In 1980, the stereo version with a dubbed section at the end for the original coda was released on the Capitol LP "Rarities".
Lastly, the stereo mix for the Apple 3-LP/2-CD commercial version of "Anthlogy 2" used a remixed version with the addition of the original solo, a normal speed vocal and an extension of the song.