did they even watch godfather 1 while writing godfather 2?

Agreed.

The screenplay has Sonny's murder occuring in the Spring of '46. But in Jenny M. Jones' book you get a glimpse of FFC's Sicilian notes that state those scenes take place in 1948.

The whole timeline is so screwed up. If the '48 clues above punctuate the timeline, then we must suppose that after murdering Sollozzo, Michael was in exile in Sicily for most of '46, all of '47, and some undetermined part of '48 (The Republican convention was held in June). So, sonny is still alive at that time as he beats up Carlo. Thus, prior to Sonny's death in '48, Vito lay in his sick bed for all of '46, all of '47, and some undetermined part of '48; possibly 2.5 years. Seems implausible.

I don't think he lay in his sick bed for two years, but the attempt on his life had severely weakened his health -- he was shot five times. I think he was already in the process of turning over complete control to Sonny. When Sonny was killed, he needed to start that process all over with Michael.

Bonasera manipulated the year on the tombstone on purpose.
The undertaker's revenge for the humiliation back in 1945.

That makes more sense than anything else I've read.

but as i explained before the massacre occurring in 50 is impossible going by the timeline

Danito was joking.

Hyman Roth pressured the Senator to give false information about the timeline during the hearings. Roth was a 1950 loyalist which is why he was killed.

Well, there wasn't enough time, Michael. There just wasn't enough time.

Was Vito lamenting that 4 or 5 years wasn't enough time, or that 8 or 9 years wasn't enough time?

Therein probably lies the answer. But there's no answer beyond anyone's own conjecture. The timeline was the weakest part of both the book and the films.

But when they wrote this stuff over forty years ago, they weren't picturing a bunch of lunatics with no lives (like us) discussing it on the Internet all day (Or as FFC famously asked Puzo during filming in 1971: What's the Internet? ).

I always wondered what Vito meant by "wasn't enough time." The novel states that it wasn't enough time for Vito to "wire" his political contacts into Michael. But, so what? He was planning to move the family to Nevada and go "legitimate."

TB, of course the novel does not contain such a scene. I think FFC put it in there as a way of conveying to the audience Vito's reluctance to involve Michael in the business. I don't think it has anything to do with setting Michael up with the politicians. I think he just meant that there wasn't sufficient time to see Michael embark on a path to become "senator Corleone".

The timeline came up on the GF Reddit sub.

They cited: https://godfather.fandom.com/wiki/Timeline

While I like the original movies ... I also like a chronological presentation for the way it flows as a more complete story.

"The Godfather 1902–1959: The Complete Epic" is a 386-minute version of The Godfather films that was released to video and includes the story - and then some - through Godfather II. (a version incorporating GF 3 was re-released in 1992)

This version, often just called The Epic, is presented as a single film and is almost 6-1/2 hours long (This is verses the 434 minute version called the "Saga" which was presented on television as 4 segments - originally aired on different nights - each with opening and closing credits).

Unlike the Saga which was released for television, the Epic contains the parts (violence and things of that sort) that were edited out for television in the Saga.

I still have a copy of The Epic on VCR tape.
(and I still have a vcr to play it on ... ahhhh, the old ways ...)

The main reason I keep my Montgomery Ward Signature 2000 Hi-Fi VCR is because I have the Saga VHS set.

A lot of stuff I recorded on VHS is now easily available on YouTube.

Yes, the "Saga" version is the definitive treatment of GF and II, chronologically ordered and with ~75 minutes of deleted scenes (every one of them great) in the right place. I bought my first VCR specifically to record the Saga, practically wore out my tapes playing it over and over again.

HBO released the Trilogy in chronological order, with deleted scenes, several years ago. I liked seeing it in hi-def and I made Blu-Ray discs of that version. But, the Saga still is the best for GF and II. Here's an example you may have noticed:

On the HBO version, and on the "Extras" disc in the DVD set, the deleted scene where Gardiner Shaw asks Michael for Sonny's daughter Francesca's hand in marriage ends with Michael shaking Gardiner's hand. But the Saga version has about 10 more seconds at the end. Michael turns to a hulking young man wearing a plaid sport coat and says, "How's the football, Santino?" "Fine, Uncle Michael," the lad replies. Santino would be Sonny's first son--his second son, Frank, is seen in GF reading a get-well card to Vito when he returns from the hospital. Small but interesting addition to Sonny's family.