There are three numbers typically used and their relationship is as follows:
% Available Chlorine (this is a weight %) < % Sodium Hypochlorite (this is a weight %) < Trade % (this is volume % available chlorine)
The second number is always 1.050 times (5.0%) higher than the first since their relationship is the weight of sodium hypochlorite (NaOCl) to the weight of chlorine gas (Cl2). The third number is the first number times the density of the product which varies by concentration but is usually around 1.07 for 5.25%, 1.08 for 6.0% (NaOCl), 1.10 for 8.25% (NaOCl), 1.14 for 10% (Trade), and 1.16 for 12.5% (Trade).
There is no way that their % Available Chlorine is 13% by volume and 10.5% by weight. More likely, if it's 10.5% by weight, then it's 12.2%, probably 12.5%. That is a pretty common Trade % for chlorinating liquid.