Where can I find "reference barcodes" to verify barcode library output?

For Code128 there isn't a single correct answer. If you use Code128-A you can get a different result than Code128-C. By result I mean how it looks. Take "803150" as an example. In Code128-A you'll need 6 characters (+ start, checksum, stop) to represent this number. Code128-C only consists of numbers, so you can compress two digits into one character. Hence you'll need only 3 characters (+ start, checksum, stop) to represent the same number. The barcodes will look different (A being longer in this case), but if you scan them both will give the correct number.

Further, Code128 doesn't need to be just A, B or C. You can actually combine the different subsets. This is common for cases like "US123457890", where Code128-A or B is used on "US" and Code128-C is used on the remaining digits. This is sometime referred to as Code-128 Auto, or just Code-128. The result is a "compressed" barcode in terms of width. You could represent the same data with A/B but again that would give you a longer barcode.

Take two online generators:

• IDAutomation
• BarcodesInc

I recommend the first one, where you can select between Auto/A/B/C. Here is an example image illustrating the differences:

On IDAutomation, Auto is default while A is default on Barcodes-Inc. Both are correct, you just need to be careful what subset you have selected when comparing output. I also recommend a barcode reader for use in development to test the output. Also, see this page for a comparision of the different subsets with ASCII values. I also find grandzebu.net useful, which has a free Code128 font you can use as well.

It sounds like your Delphi library always use Code128-C, since it's only possible to represent numbers in this subset.