Timeline/Inconsistencies

Throughout JoJo's Bizarre Adventure, there are a few cases where the timeline does not match up with previously stated dates or dates end up being changed in future chapters, creating inconsistencies.

Date of Stardust Crusaders
One of the largest contradictions in the series is the date that Stardust Crusaders took place. Stardust Crusaders has a journey taking fifty days, beginning either in the end of 1987 and concluding in the start of 1988, or beginning in the end of 1988 and concluding in the start of 1989.

1987-1988
1987 is used in JoJo6251, the anime, and a few times in the Diamond is Unbreakable manga. It is never explicitly stated in the Part 3 manga.
 * Josuke is said to be born in 1983 and was four years old when he gets his fever.
 * In the anime, Keicho states that his dad starts mutating when DIO was defeated eleven years ago in 1988, when Okuyasu was four years old.

1988-1989
1988 is used in the Part 4 manga and Part 6, with several things in Stone Ocean being based on Part 3 taking place in 1988.
 * Jotaro hasn't stopped time in 10 years, meaning since his battle against DIO in 1989 since Part 4 takes place in 1999.
 * Jotaro says DIO got his stand in 1988. He and Keicho also say the battle against DIO occurred "10 years ago". Keicho mentions that Okuyasu was five years old at this time in the manga, which is inconsistent since Josuke was four when he got his fever.
 * Pucci was born in 1972 and was 16 when meeting DIO, who he says he met in 1988. The two have met more than once, which wouldn't be possible if DIO died in early 1988 as DIO would have to travel back and forth from Florida to Egypt.
 * Pucci says that Jotaro burned DIO's diary in 1989 after he defeated DIO.

Jotaro's Age

 * Jotaro is 28 in Part 4 (1999-28=1971, 1971+17=1988) and 40 in Stone Ocean (2011-40=1971). However, his birth date is said to be 1970 in JoJo6251. Considering his manga biography also states that his zodiac sign is Aquarius in Part 3, his birthday would be in either January or February and Part 4 takes place in April, meaning he should actually be 29.
 * The anime attempts to keep the date consistent with the year Part 3 took place being 1987, but they keep Jotaro's age being 28 in Part 4. His birth year and zodiac were never stated in the anime, so his birthday may just end up being later in the anime timeline.

Koichi's Age
Koichi is said to be 18 in 2001 (Chapter 454) when he is supposed to be 17 as his birthday is in March, 1984.

Narancia's Age
Narancia was originally born in 1984 with a Leo zodiac sign in Chapter 472. This date and zodiac is kept in the anime, despite his birthday later being changed to May 20, 1983 with a Taurus zodiac sign in Chapter 572.

Trish's Age
In Chapter 540, Trish's birth date is April 14, 1986 but in Chapter 591, it is changed to June 8, 1985.

Steel Ball Run Dates
Stage 8 starts on December 28, 1890 and is said to last 2 days, whereas the final stage afterwards lasts approximately 30 minutes. However, the date is somehow January 19, 1891 by the time the race finishes.

JoJolion Ages
Tsurugi was originally 2 years old in the Ultra Jump release of JJL Chapter 7, but was corrected to 9 years old in the volume release. He later becomes 10 years old throughout the story.

Joshu was originally 18 years old and then says he's 19 in JJL Chapter 57. While Tsurugi's age has changed from nine to ten years old in the character biographies in each volume, Joshu's age remains as 18.