That's because you didn't enter the numbers the way it works in PTO/Lacerte.  The 2017 statement includes information about excess limitation for each year, which I agree comes in handy but is not a requirement from a reporting standpoint; it is there only for reference.

While PTO/Lacerte doesn't provide any information about excess limitation in prior years (and it took a bit of getting used to that when I first started using it), you can still easily tell there is no room for carryback if there is an amount shown under the column "Foreign Tax Credit Carryover".

Now back to your question specifically.  Could you help me understand your client's situation a bit better?  Was (1) 2017 your client's first year in a fiscal year country (or a no tax jurisdiction) before any tax was assessed and a ***substantial*** amount of his foreign earned income couldn't be excluded by §911 or (2) your client resided in the US but traveled extensively for work overseas in 2017 or (3) your client exercised NQSO or had disqualifying disposition of ISO in 2017 and a large part of it was related to prior year assignment(s)?  The reason I asked is that it would otherwise be unusual to have such a large excess from 2017, particularly since there was no foreign tax paid (and any scaledown).

Assuming nothing is amiss, here's how you should have made your input -
Credits > Foreign Tax Credit C/O (1116) > General Limitation Income: Nothing since there are only excess limitations or FTC carryover.
Credits > Foreign Tax Credit C/O - AMT (1116) > General Limitation Income:  Since the 2017 statement doesn't show all the details, I'd make up some numbers to arrive at the same results just for illustration purposes -

If you were preparing a ***2017*** return in PTO, you'd make your entry as follows -  
2015
====
Foreign Tax Paid = $123,456
Foreign Tax Disallowed = $45,000
Foreign Tax Claimed = $53,852
Foreign Tax Carryover = $24,604

2014
====
Foreign Tax Paid = $112,050
Foreign Tax Disallowed = $52,427
Foreign Tax Claimed = $48,679
Foreign Tax Carryover = $10,944

Since the carryover from 2015 and 2014 were used up on the 2017 return, the C/O entries proforma'd (or manually input by you in the case) for 2018 would look like this -
2015
====
Foreign Tax Paid = $123,456
Foreign Tax Disallowed = $45,000
Foreign Tax Claimed = $78,456
Foreign Tax Carryover = $0

2014
====
Foreign Tax Paid = $112,050
Foreign Tax Disallowed = $52,427
Foreign Tax Claimed = $59,623
Foreign Tax Carryover = $0