If i had to guess, I'd say its probably just the brand of almonds... then again i have basically no experience with weight measuring. I use my handy dandy 1/4 cup for measuring my almond portions (if it means anything, that usually comes out to around 30 almonds)
hopefully someone else can give you a more 'sure' answer.
I have those 100 calorie packs of almonds and there are about 20 in there, per 18g bag. So 1 ounce probably is about 30. But if you weigh them then just go by weight, take whatever comes out from weighing 1oz.
Who cares how many there are in an ounce? An ounce is an ounce and if that means 5 big ones or 32 little ones it's the weight that matters in calorie counting. Just keep weighing them everytime.
I've used two brands of almonds. One says that 12 almonds = 100 calories. The other says 10 almonds = 100 calories. There is a noticeable difference in the average size of the nuts.
You can make this hard and drive yourself insane, or you can make it easier.
About 22 or 23 raw almonds = a 1 ounce serving, more or less. That amount contains 164 calories, more or less. Just count out the almonds. Sometimes you'll have more than 164 calories, sometimes less, but it will all even out. Heck, round it to two dozen if that feels better and use 170 calories.
I buy the Market Pantry plain raw almonds - they are 32 for an ounce. I got the Blue Diamond plain roasted once and they weighed to only 24 for an ounce. I made notes of how many for what type of almond, and I typically only buy those two kinds, so I just count out what I expect. If I get a new brand I weigh or not, depending on how I'm feeling. If I don't feel like weighing I go with the 22-23 number.
How many are in an ounce really doesn't matter, an ounce is an ounce. Just weight them out and throw them in little zip lock bags. 1 oz (28 grams) = approx 160 cals. I buy my almonds in bulk and as soon as I get home I weight them into serving sizes, put them in zip lock bags and put them somewhere in eye sight so when I'm searching for a safety food, they are there ready to eat.
This is why it is so important to weigh your foods.
I just had the new Special K crackers with a tuna snack for lunch and although it says 17 crackers is the serving.. truly after I weighed I was able to have 20.
If one ounce is what you are aiming for when figuring your almond calories.. just go with what your food scale says and you will be fine. Don't worry about the actual number of almonds.
I prefer weighing whenever I can, because calories by weight are virtually always more precise and accurate than calories by other forms of measurement. The least precise, I've found is the counts. I've almost never had the ounce (or whatever weight measure listed on the nutrition label) measurement contain the same number of chips, crackers, nuts ..... as the nutrition label estimates.
When my scale isn't available, I do use the count measurement. I use an exchange plan, so my nut serving is 1/4 ounce (usually about 6 nuts - but it does vary depending on the size of the nuts).
how many almonds in a serving
But if you weigh them then just go by weight, take whatever comes out from weighing 1oz. 
