  The INTEGRAL SPI instrument observes the hard X-ray sky from 20 keV up to a
few MeV since more than 15 years. In this energy domain, the main emitters are
compact objects for which SPI provides spectral information of prime interest.
Recently, two transient sources reached very unusual flux levels and have been
detected up to a few hundreds of keV with a high significance level. A drastic
reduction of the systematic errors is thus required to obtain reliable spectra.
This objective is achieved through an analysis including a detailed
understanding of the instrument behavior. This paper presents both aspects of
the data analysis: we first give a basic description of the instrumental
issues, then we present the solution to be implemented in the SPI data analysis
(at the event selection stage) and illustrate with a few examples the
reliability of the SPI results in the high-energy domain when the data analysis
is performed properly. We take benefit from this refined analysis procedure to
propose an updated model of the hard X-ray spectral shape of the Crab Nebula.
We revisit the high-energy emission observed in GS2023+338 spectra during its
2015 outburst and present the first results from the SPI observations dedicated
to the recently discovered transient MAXI J1820+070.
