Hi. My name is*****'m looking at your question now and will post my answer or ask for more information here in a short while.
I'm not sure what you mean by "does this reduce the threshold for the current year ?".
If your income, not just earnings, for a tax year is over £100,000, you lose £1 of the personal allowance for every £2 of income over £100,000. If, however, you pay a pension contribution the gross contribution reduces your "adjusted net income" for the purpose of determining your entitlement to any, all or none of the personal allowance. So, for example, if your income is £110,000 and you pay a net pension contribution of £8,000 (£10,000 gross), then your adjusted net income income will be £100,000 and you will keep all your personal allowance. It makes no difference whether the pension payment you make includes an element to cover unused relief from an earlier tax year. Look here for information on adjusted net income.
I hope this helps but let me know if you have any further questions.
There is information on the annual allowance here.
You cannot backdate a pension contribution. You can make a pension contribution in the current tax year which includes unused annual pension allowance from the three previous tax years. Tax relief will be given in the current tax year.
You ought to check with your pension provider exactly what you can do.
As your income for 2016/17 will be high, the annual allowance for that year will be £10,000 according to the information in the link I gave you. You still have unused annual pension allowance for earlier tax years but you should check with your pension plan provider to find out what that is as that will be the figure you can add to the 2016/17 annual allowance of £10,000 and determine what the highest payment you can get tax relief on is for 2016/17.
I've seen many cases where individuals have paid too much in pension contributions and had to pay an annual allowance charge to HMRC. All that has to be done is for the individual to ask their pension plan provider for a breakdown of unused relief for earlier years and to add that to the current year's allowance which in your case is £10,000. You say you have £60K from earlier years so just to be sure, check that with your plan provider.