Hi,

I'm not sure where you are getting your information from, but as I told
before I actually *own* this board in the non-development version and it
has an RK3528 SoC/silkscreen - I just was too lazy to photograph it my own
but I did now [0]

I have the MangoPi M28S, M28K and M28C boards.
The M28K board does have a silkscreen of RK3528A. [2]
Regardless of whether the silkscreen is RK3528 or RK3528A,
U-Boot reports that the SoC on these boards is RK3528A. (via OTP [1])
So one possibility is that Rockchip forgot to update the silkscreen.

Comparison chip block diagram:
1. Earlier version: https://docs.armsom.org/img/sige/rk3528.png
2. Final   version: https://docs.radxa.com/img/e/e20c/radxa-e20c-chip-diagram.webp

The difference seems to be that RK3528 uses I2S while RK3528A uses SAI.
But from the updated diagram here [3], RK3528 also uses the SAI interface.

Rockchip BSP does not make any distinction between RK3528 and RK3528A,
so it is meaningless to continue to worry about non-A versions.

[1] https://github.com/u-boot/u-boot/blob/master/arch/arm/mach-rockchip/rk3528/rk3528.c#L131
[2] https://x.com/mangopi_sbc/status/1847851624804602316?t=5hwScxgwCAAid0eCJgrP5w&s=19
[3] https://x.com/mangopi_sbc/status/1785115827437760769?t=H5PXRDwbjOfBYa7QotjIZw&s=19

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2.25.1