Hi,
The diodes are there and they are real. The reason that they are not documented beyond that, is that they are matched.
Consider this model:

The Error Amplifier, EA, has three inputs. There is the reference input, the soft start input and the feedback node, Vsense.
The EA will regulate the lowest of the two voltage, the fixed reference (7.5V) and the voltage on the SS pin.
When the voltage on the SS pin is greater the 7.5V the reference in the controlling input.
D1 and D2 are needed to OR the fixed reference and the soft start inputs.
The voltage at the non-inverting input of the EA is lower of the two inputs plus one diode drop.
D4 add the diode drop to the Vsense input.
The diodes are biased by the input currents of the EA.
Modelling Result
General CommentsYou would be much better using an IC that is designed to be an LED driver, like the LT3799, instead of adding work arounds to a PFC chip.
Given the other topics that you have started on the EEVBlog in the last few weeks, I am sure that you are not designing a battery charger. You would get much better help if you told the truth and asked for help for an LED driver.
Regards,
Jay_Diddy_B