Fitbit?

Exercise depends.

HR-based calorie burn formula is only a decent estimate for steady-state aerobic exercise same HR for 2-4 min.
And even then their are caveats that cause inflated HR readings above what would normally be needed - dehydrated, long into the workout or a very hard prior workout, stressed for other reasons beyond that.

So intervals or anything with HR bouncing all over the place will be inflated calorie burn calculation.

That being said, was that a hard 30 min 3x weekly of inflated calorie burn among an otherwise active week?
In which case the allowed inaccuracies on food labels would be off more than that inflation.
Or was it 60 min 6x weekly among a very sedentary lifestyle otherwise (no kids, pets, household duties, bump on a log day and night outside exercise)?
In that case the inflated amount could add up.

If you are out of shape your HR may be bouncing up high enough to make the device think this is a workout and start doing HR-based calorie burn - and you are only walking normally for daily things - but again - how frequent?

Just in case if by allotted exercise calories you mean the Fitbit Adjustment that happens to show up under the Exercise Diary - that's not just exercise, or even any perhaps.
It's merely the difference between what Fitbit reports as daily burn minus what MFP estimated for daily burn with no exercise and your perhaps underestimated daily activity level.
Could have big adjustment and no exercise just very active that day.
Could have no adjustment and really hard workout but slept longer that day.

I have had my Fitbit synced since mid-2015. By comparing it to my long-term trends, I have found that it is reliable for me.

I'm using the FitBit Charge 3 and have since starting my diet on 1/28. I mostly use it to self-evaluate where I am and make sure that my TDEE and exercise get recorded in some way. It also is nice having it prompt me to get up and move around every hour and check my sleep. I like it well enough I bought my mom one.