Good news! I found a commercial site ([Link: premisesystems.com]) with a rather large database of IR codes, including many RC5 codes. There I was able to find RC5 codes that work for all but one of my original remote's buttons.

What's interesting is that when I enter the RC5 codes, Pronto converts them into the longer strings that were being learned from my original remote-- but these converted strings work! The same codes never worked when learned or when entered directly. They only work when entered first in RC5 format. Not knowing enough about the Pronto's internals, I can only conclude that Pronto can correctly set itself up to use parity bits when the code is entered as RC5 -- maybe that detailed information is elsewhere on this site.

Anyway, here are the RC5 codes I was able to find -- for those who might be having trouble with a Philips Smart Series TV:

digit 0 5000 0072 0000 0001 0000 0000
digit 1 5000 0072 0000 0001 0000 0001
digit 2 5000 0072 0000 0001 0000 0002
digit 3 5000 0072 0000 0001 0000 0003
digit 4 5000 0072 0000 0001 0000 0004
digit 5 5000 0072 0000 0001 0000 0005
digit 6 5000 0072 0000 0001 0000 0006
digit 7 5000 0072 0000 0001 0000 0007
digit 8 5000 0072 0000 0001 0000 0008
digit 9 5000 0072 0000 0001 0000 0009
TV POWER 5000 0072 0000 0001 0000 000C
MUTE 5000 0072 0000 0001 0000 000D
STATUS/EXIT 5000 0072 0000 0001 0000 000F
VOLUME ^5000 0072 0000 0001 0000 0010
VOLUME v 5000 0072 0000 0001 0000 0011
SMART SOUND/ENTER 5000 0072 0000 0001 0000 0014
SMART PICTURE 5000 0072 0000 0001 0000 0015
TV ^ 5000 0072 0000 0001 0000 001C
TV v 5000 0072 0000 0001 0000 001D
CC5000 0072 0000 0001 0000 001E
TV CH ^ 5000 0072 0000 0001 0000 0020
TV CH v 5000 0072 0000 0001 0000 0021
A/CH 5000 0072 0000 0001 0000 0022
Incredible Stero5000 0072 0000 0001 0000 0024
Sleep5000 0072 0000 0001 0000 0026
TV >/+ 5000 0072 0000 0001 0000 002B
TV 5000 0072 0000 0001 0000 002C
Menu 5000 0072 0000 0001 0000 002E
PIP POS5000 0072 0000 0001 0000 002F
PIP FREEZE5000 0072 0000 0001 0000 0036
PIP SWAP5000 0072 0000 0001 0000 0037
TV TV/VCR 5000 0072 0000 0001 0000 0038
AV (source)5000 0072 0000 0001 0000 0038
PIP ON/OFF5000 0072 0000 0001 0000 003A

The button for which I could not find an RC5 code is the PIP Source button. The longer code learned by Pronto is as follows:

0000 0073 0000 000D 0040 0020 0020 0020 0020 0020 0020 0020 0020 0020 0020 0020 0020 0020 0020 0040 0020 0020 0020 0020 0020 0020 0020 0020 0020 0CAC

If anyone knows an equivalent RC5 code for this or the alternate long code, please post it. Thanks!