General Hardness Gh - Difference Between Water Supplier & Test Kit Results

My water supplier quotes 17dh, and with the Columbo kit it comes out at 16dh, so not a huge difference for me.
As far as which one you should go with when choosing fish there are several things that can be taken into account:-
Had your water sample been left to sit or was it taken straight from the tap - does temperature of sample effect the results? (I didn't check this one)
Does your tank decor impact the water parameters - wood, plants, leaf litter, limestone, etc. They may only be slight changes but they all add up and worth noting.
Water hardness ranges quotes for specific fish - there is always a range, and fish may be better off mid-range, but will be ok within the range or slightly outside the range. There may also be different information on different sites, or some sites may use soft/medium/hard rather than numbers, and if there is no key to what they mean, or globally accepted ranges for those words, then it is open to interpretation. I have previously canvassed opinion on this forum and at various stores (mainly to justify my purchase of my bn & bea). People do keep fish outside stated water parameters (my water is 17dh, bristlenose plecs range stated up to 12dh), with people on the forum and at stores finding it generally acceptable to have this difference as long as fish health & behaviour, as well as water quality, is monitored.
Commercially farmed fish v wild caught - farmed fish probably more tolerant to different water parameters depending on where they have been farmed and the parameters of the water there. Most water parameters stated for fish are for wild, although most will mention if commercial available fish are more tolerant.
Sorry to not give a straight forward answer, but it is a very personal thing. I keep fish that should be in softer water than I have, and I am ok with that. Some people would consider this irresponsible, some people would consider it acceptable.
If I were in your shoes, I would go with what the water supplier is quoting because they will have to be testing the water with equipment which is calibrated and maintained to internationally recognised standards, and they have to be held accountable for water that is deemed fit for human consumption, which will be more heavily regulated than water for the aquatics industry. So I would go with a level of 16dh, but find it acceptable to have fish that are commercially farmed and probably more tolerant to parameters outside their stated range.
Hope that confusing & rambling explanation helps, if you can make sense of it.