数値 and 数字: measured values and numerical notation
Compare 数値 for a numerical value with 数字 for digits or contextual figures, including sales figures that are not identification numbers.
A value obtained by measurement
数値, read すうち, means a numerical value. 測定した数値を表に入力しました。 says that measured values were entered into a table. Both measurement and entry occurred.
長さの数値は五です。 gives a length value of five without identifying its unit. Five centimeters and five meters represent different lengths.
Digits and contextual figures
数字, read すうじ, means numbers or digits. 紙に書かれた数字を順番に読み上げた。 says that the numbers written on paper were read aloud in order. Context identifies what they represent.
In 売上の数字だけでは店の良さは測れない。, 数字 refers to sales figures. Restricting it to identification numbers would miss this use.
Read the quantity and its unit
For 数値, identify the measured quantity; for 数字, identify the notation or figures being discussed. Their uses can overlap when referring to numerical figures.
表の数字を確認してください。 requests a check of the numbers in a table. It does not already establish that values were entered incorrectly.
Does 数字 in 売上の数字 necessarily mean product identification numbers?
Show the answer and why
No. Here it refers to sales figures. 数字 can denote numerical notation or figures supplied by context.