using correct -l -L and -I flags with cc still leads to undefined reference

Question

I'm working with a Makefile that issues the following command:

cc -g -O -I/opt/local/include -lsndfile -lm -lpvoc -L/opt/local/lib/ -L/usr/lib/x86_64-linux-gnu/   -c -o fileio.o fileio.c

followed by eventually:

cc -o plainpv -g -O -I/opt/local/include -lsndfile -lm -lpvoc -L/opt/local/lib/ -L/usr/lib/x86_64-linux-gnu/  plainpv.o -L../PVC_LIB -lsndfile -lm -lpvoc -L/opt/local/lib/ -L/usr/lib/x86_64-linux-gnu/

but that results in the following error:

../PVC_LIB/libpvoc.a(fileio.o): In function `getInputFileDataToSetOutputChannels':
/home/meeshkan-abel/Downloads/PVCplus.Beta.Public.Distribution.5-25-2017/PVC_LIB/fileio.c:63: undefined reference to `sf_open'
/home/meeshkan-abel/Downloads/PVCplus.Beta.Public.Distribution.5-25-2017/PVC_LIB/fileio.c:168: undefined reference to `sf_seek'

even though both of these functions are in libsndfile. I'm wondering why, even though libsndfile is linked when building fileio and when building plainpv, there are still undefined reference errors. Usually I see these when forgetting to link to a library, but it seems like the linking is correct here. Any thoughts on where to investigate? Thanks!