It is best to always ensure you know WHY all the adjustments to your tax code have taken place before you submit a tax return, it may very well be that the adjustments will point out a matching adjustment that is needed on your tax return.If I submit SA now would I be too late for them to adjust my code? I would need to pay £147 before end of January is my understanding.
eg its possible some expected tax owed was coded out to a later tax year and there would be a matching adjustment needed on the actual return.
eg there could be flat rate job expenses - or expected actual job related expenses have been included in your tax code - if that's the case you need to decide whether you can make the claim the tax office are expecting on your return (or similar as appropriate ) - or whether you are happy its an incorrect hmrc assumption in which case you submit the return as it is and pay the tax.
Unfortunately its not beyond the realms of possibility you could owe tax for earlier years - if for example you made a one off claim years prior for job related expenses and hmrc increased your tax code on the basis the claim would be repeating.
Tax code notices really should come with a big red warning that ignoring them or presuming they are correct can result in you underpaying tax with the associated later implications that as far as they are concerned its your fault if it turns out this error carries on well into the future and you have backdated tax owed that you should have flagged up earlier.