Why does “/proc/config.gz” show wrong configuration?

I should have done more research prior to posting this question, but I thought might be I was missing something. For reference, the problem reveals to be specific to my kernel source. Custom kernel developer applied a patch to always include an older configuration in kernel binary. So this should be undone (considering the risks, if any):

ifeq ($(CONFIG_MACH_XIAOMI_MIDO),y)
    $(obj)/config_data.gz: arch/arm64/configs/mido_defconfig FORCE
else ifeq ($(CONFIG_MACH_XIAOMI_TISSOT),y)
    $(obj)/config_data.gz: arch/arm64/configs/tissot_defconfig FORCE
else
    $(obj)/config_data.gz: $(KCONFIG_CONFIG) FORCE
endif