LOINC Results Codes - Why so many?

LOINC apparently contains numerous codes for the same lab results. Can someone help me understand why this occurs in the context of the following example?

Filtering for Component “LDL” creates for me the following questions:

1)Why are there multiple codes corresponding to the same test, with the same name?

a. 14 “Cholesterol.in LDL” components

b. 14 “Cholesterol.in LDL 1….7” components

2)What is the difference between these results?

3)Why are the majority of codes apparently not used?

a. Common_Test_Rank shows only 3 codes used for results

b. Common_Order_Rank shows only one-code used for ordering

c. Common_SI_Test_Rank returns 3-different codes

i. What are SI Tests?

  1. Are they research related?

4)Anything else I should know?

Thanks in advance!