As summer break is coming up, you have started to misbehave in school, getting sent to detention quite often.
On June 20th, something interesting happened, and made detention a little more fun. You noticed that one of the tiles on the floor was loose, and that a small piece of paper was sticking out. When your teacher left for his daily refilling of his coffee, your curiosity got the best of you, and you hopped out of your seat and took the piece of paper. Later at home you inspected the piece of paper. On it were the words:
Yusiecnjhuqouqornl pljgcatpnokizvtuqoxtr'yus jfduqotpn'zvt migkgezvt vrpgcaokijfd kgetpnuqoawumignjh okitpn someay uqovrpokitpnokiuqotpn. - Somxtr. Pljkgetpnqmkokitpnyus
You have no idea what it means, and decide to investigate further.
Worrying, as tomorrow is the last day before school ends, you spend all night thinking and analyzing, but come up with nothing. You go to school the next day, make sure you get in detention, and then grab the last message before summer. This message says:
Yvsifcnkhurourorol pmjgdatqnolizwturoxur'yvs jgdurotqn'zwt mjgkhezwt vspgdaolijgd khetqnuroaxumjgnkh olitqn spmeby urovspolitqnoliurotqn. - Spmxur. Pmjkhetqnqnkolitqnyvs
You spend the first week of summer constantly studying the notes, but still can't figure it out. In August, fed up with not knowing, you ask your friend in summer school to sneak in and grab you the notes. The note he gives you on August 6th reads:
Ayskicpnhwuowuotrl rpjigavtnqoibztwuozxr'ays ljdwuovtn'bzt omgmkebzt xvpigaqoiljd mkevtnwuocauomgpnh qoivtn usmgey wuoxvpqoivtnqoiwuovtn. - Usmzxr. Rpjmkevtnsqkqoivtnays
Looking at the old and new notes with fresh eyes, you solve the puzzle.
What do each of the messages say?
After revisiting the messages you realize two things that you should've seen earlier that would've helped you. One is fairly obvious and one is more obscure. These things are:
The messages are all of exact length and have the exact same punctuation, meaning they are all likely the same message, but coded in a different way.
The messages rely on the date they were written to be solved.
Solution with explanation (In response to user45266 and all users who answered):
The reasoning behind this cipher was for me to test my Java programming skills. I wrote a program to encode and decipher text, and this was the cipher that I used. It works like this:
Take the input string of characters, and turn each letter into three of itself (e.g. "a" to "aaa", or "f" to "fff"), avoiding punctuation and numbers and all non-letters. This step is just to make the output longer than the input to create confusion (although not very well).
Take the date of the message (MM/DD/YYYY) and add the individual numbers together (e.g. June 21st, 1997 = 06/21/1997 = 0+6/2+1/1+9+9+7 = 6/3/26)
Rotate the first letter by the first number, the second by the second, and so on (e.g. aaa = gda, fff = lif)