
Samsung Galaxy Core Plus
The latest firmware for Samsung Galaxy Core Plus (SM-G3502) is G3502ZNUANG1 with Jelly(Android Bean), released on August 5, 2014 for 1 region (CSC). Every official firmware build for SM-G3502, newest first: one row per build with all regions (CSC) that received it.
Each firmware build has its own page at https://samfirm.shop/build/{PDA}, where {PDA} is the build number from the list above. Example: https://samfirm.shop/build/G3502ZNUANG1
The newest build, G3502ZNUANG1, was released on August 5, 2014. No new build has appeared for 148 months, so regular updates for this model have most likely ended.
Specifications of SM-G350, a regional variant of the same device. Chipset and SIM lines are left out: they can differ by region.

SM-G935TZK

SM-G930AZK

SM-G935AZS

SM-G935TZS

SM-G935AZK

SM-G935TZD

SM-G975WC

SM-G975FC
The latest build for SM-G3502, G3502ZNUANG1, was released on August 5, 2014 (12 years ago).
SM-G3502 has had no new firmware for 148 months, so regular updates have most likely ended.
Yes, all firmware files for SM-G3502 are 100% official, original, and obtained directly from Samsung servers.
To flash SM-G3502, you need to download the appropriate firmware, put your device into Download Mode, and use the Odin tool to load the BL, AP, CP, and CSC files.
Downgrading is only possible if the bootloader version (binary bit) of the old firmware matches the current one. Always check the binary version before flashing SM-G3502.