Yeah 90 means 90000yen which was the price and therefore spec description, ie it's a good one.
I don't think 89 on sn signifies anything other than it being part of the unit number that this bass is as part of all the E series instruments across all ranges.
Time wise it's 84-87 as when the E series was in production.
I've had 2 E series basses and both were really well made and played as great as their reputation suggests.